This invention relates generally to an electrophotographic printing machine, and more particularly concerns a boundary layer disturber for cooling a glass platen for such a machine.
In conventional copying or scanning machines, an original document to be reproduced is placed or conveyed onto a glass platen located in the object plane. The document is incrementally illuminated by an elongated lamp assembly, either by moving the platen while the lamp is held stationary, or by moving the lamp assembly (lamp reflector and scan mirror) beneath a stationary platen. Alternatively, both the scan lamp and the platen can be held fixed and the document moved across the platen surface in a continuous velocity transport (CVT) mode. In any of these cases, a problem to be anticipated and prevented is a buildup of heat at the platen, the heat being a byproduct of operation of the scanning lamp. The lamps used for document scanning are typically mercury fluorescent or tungsten halogen. With either source, but particularly with the tungsten halogen type of lamp, the heat buildup at the platen may pose a problem with continued operation. With continued usage, the platen may become so hot as to present a safety concern for the machine operator or cause defects in the platen glass.
Conventional copying machines employ large and noisy blowers in an optics cavity to reduce the heat buildup of platen glass. The blowers provides cooling of lamp, reflector, and optics base pan contained in the optics cavity. Also, the blowers provide pressurization of the optics cavity as to prevent processor dirt and ambient dirt from contaminating sensitive optical components. And, it has been found that the thermal boundary layer, which is a thin layer of heated air closely adjacent to the lower surface of the platen, tends to be difficult to remove with standard convection methods.
Various other approaches have been devised to increase platen glass cooling, the following disclosure appears to be relevant:
U.S. Pat. No. 4,945,383 discloses an image forming apparatus which includes a temperature control device to control the temperature of light on a photosensitive medium. The apparatus is comprised of a pair of cooling fans and a heat ray reflecting shutter. The heat ray reflecting shutter aids in the ventilation created by the fans.
U.S. Pat. No. 4,632,539 discloses an apparatus for cooling a fluorescent lamp by causing a flow of cooling air to pass along a conduit extending along the length of the lamp.
Even with the above mentioned teaching available, the problem with heat build up on the platen glass remains.